1. Field of the Invention
The present invention relates to a reflow soldering apparatus and a reflow soldering method for soldering electronic components on a circuit board by sending the circuit board with electronic components mounted thereto through a heating furnace.
2. Description of the Related Art
In a reflow soldering apparatus, a circuit board and electronic components are heated, thereby melting a solder to join the circuit board and electronic components by the solder. A high reliability has been demanded recently in judging whether the circuit board is transferred normally or abnormally in the reflow soldering apparatus to prevent overheating of the circuit board and the electronic components during the transfer.
A conventional reflow soldering apparatus will be described with reference to FIG. 12. In a conventional reflow soldering apparatus 1 shown in FIG. 12, 2 is a circuit board, 3 is a circuit board transfer conveyor, 4 is a controller, 5 is a reception side of a transmitting type sensor, and 6 is a projection side of the transmitting type sensor. Operation of the reflow soldering apparatus in the constitution will be described below.
The circuit board 2 carried in from an entrance side 7 of the reflow soldering apparatus 1 is transferred to an exit side 8 of the reflow soldering apparatus 1 by the circuit board transfer conveyor 3. If the circuit board drops from the circuit board transfer conveyor 3 while being transferred, the reception side 5 and projection side 6 of the transmitting type sensor detect the dropped circuit board 2, with outputting a signal to the controller 4.
Meanwhile, a publication No. 4-356352 of Unexamined Japanese Patent Application discloses a reflow soldering apparatus which has circuit board-detecting sensors arranged at an entrance and an exit, and circuit board surface temperature-detecting sensors arranged via a constant interval thereinside. It is monitored whether the sensors are turned into an off state within a fixed time after having been an on state in consequence of detecting the circuit board, thereby detecting whether or not the circuit board is caught in the middle of the transfer.
In the above constitution of the reflow soldering apparatus 1 shown in FIG. 12, only the drop of the circuit board 2 is detected and a jam of the circuit board in the middle of the transfer cannot be detected. Also, since the transmitting type sensor is used to detect the drop, the apparatus 1 has a problem that the circuit board 2 that is detectable in the apparatus is limited in terms of a thickness by a light projection width from the transmitting type sensor.
Further the invention disclosed in the published specification No. 4-356352 cannot detect the drop.
The object of the present invention is therefore to provide a reflow soldering apparatus and a reflow soldering method with which an abnormality in transfer of circuit boards can be detected with high reliability, with solving the above problems.
In order to achieve the aforementioned objective, according to a first mode of the present invention, there is provided a reflow soldering apparatus comprising:
a transfer conveyor for transferring a circuit board with electronic components from an entrance to an exit of the reflow soldering apparatus having a heating furnace through which the circuit board mounted is passed so as to operate reflow soldering to the electronic components on the circuit board;
an exit-side circuit board detect sensor arranged at the exit for detecting that the circuit board transferred by the transfer conveyor is carried into the reflow soldering apparatus;
a discharge conveyor arranged below the transfer conveyor for discharging a dropped circuit board dropped from the transfer conveyor during the transfer by the transfer conveyor from an inside to an outside of the reflow soldering apparatus;
a discharge completion detector arranged at an exit side of the discharge conveyor for detecting that the dropped circuit board transferred by the discharge conveyor is discharged to the outside of the reflow soldering apparatus; and
a control device which judges based on information from the exit-side circuit board detect sensor whether or not the circuit board is transferred by the transfer conveyor from the entrance to the exit, controls the discharge conveyor to discharge the dropped circuit board when judging occurrence of transfer abnormality, determines that the transfer abnormality is the drop of the circuit board when the discharge completion detector detects the dropped circuit board, and then continues the reflow soldering when determining the drop.
In an arrangement of the reflow soldering apparatus, in the case where a plurality of circuit boards are carried to the entrance in a single line, the control device may determine that the transfer abnormality is a jam of the circuit boards at the transfer conveyor and then lowering a temperature of the heating furnace when the discharge completion detector does not detect discharge of the dropped circuit board and moreover the exit-side circuit board detect sensor does not detect discharge of the circuit board.
The reflow soldering apparatus may further comprise an entrance-side circuit board detect sensor arranged at the entrance for detecting that the circuit board is carried into the apparatus, wherein the control device has a transfer estimate time necessary for the transfer conveyor to transfer the circuit board from the entrance to the exit, so that the control device judges presence or absence of the transfer abnormality on a basis of whether or not the exit-side circuit board detect sensor detects discharge of the circuit board within a circuit board detect time after the transfer estimate time has passed, the circuit board detect time corresponding to a passing time of the circuit board in a transfer direction of the circuit board detected by the entrance-side circuit board detect sensor.
In the reflow soldering apparatus may further comprise an entrance-side circuit board detect sensor arranged at the entrance for detecting that the circuit board is carried into the apparatus, wherein, in the case where a plurality of circuit boards are carried to the entrance in a single line, the control device judges presence or absence of the transfer abnormality based on a comparison between a carry-in interval of adjacent circuit boards detected by the entrance-side circuit board detect sensor and a discharge interval of the adjacent circuit boards detected by the exit-side circuit board detect sensor.
The reflow soldering apparatus may further comprise an entrance-side circuit board detect sensor arranged at the entrance for detecting that the circuit board is carried into the apparatus, and
a counter device in which a circuit board count set value is defined and which adds one when the entrance-side circuit board detect sensor detects the circuit board and subtracts one when the exit-side circuit board detect sensor detects the circuit board, the circuit board count set value corresponding to the number of circuit boards which can be presented between the entrance-side circuit board detect sensor and the exit-side circuit board detect sensor,
so that the control device judges presence or absence of the transfer abnormality on a basis of a comparison between the circuit board count set value and a counted circuit board value by the counter device.
Further according to a second mode of the present invention, there is provided a reflow soldering method comprising:
judging whether or not a circuit board with electronic components mounted thereon is transferred by a transfer conveyor from an entrance to an exit of a reflow soldering apparatus with a heating furnace for operating reflow soldering to the electronic components on the circuit board by passing the circuit board through the heating furnace;
detecting, when presence of transfer abnormality is judged, whether or not a dropped circuit board dropped from the transfer conveyor while being transferred by the transfer conveyor is discharged to an outside of the apparatus by a discharge conveyor arranged below the transfer conveyor;
determining, when the dropped circuit board is detected to be discharged by the discharge conveyor, that the transfer abnormality is the drop of the circuit board; and
continuing the operation of the reflow soldering.
In the reflow soldering apparatus according to the first mode and the reflow soldering method according to the second mode of the present invention, the transfer conveyor, the exit-side circuit board detect sensor, the discharge conveyor, the discharge completion detector, and the control device are comprised in addition to the heating furnace for soldering. Whether or not the circuit board is transferred by the transfer conveyor is judged, and the discharge conveyor is started when an abnormality in the transfer is judged. After the start of the discharge conveyor, when the discharge completion detector detects that the dropped circuit board is discharged, the transfer abnormality is determined to be the drop of the circuit board and the reflow soldering is continued. Thus it can be detected whether the circuit board transfer abnormality in the reflow soldering apparatus is the drop of the circuit board or the clog of the circuit board. The transfer abnormality is thus detected with high reliability.
Since the heating furnace is decreased in temperature when the circuit board clog is judged, the clogged circuit board is prevented from being excessively raised in temperature.
Further, in the reflow soldering apparatus according to the first mode, since presence or absence of the transfer abnormality is judged on the basis of the transfer estimate time, the transfer abnormality of the circuit board can be detected irrespective of a thickness of the circuit board.
Further, in the reflow soldering apparatus according to the first mode, when the judgment is based on the comparison between the carry-in interval and discharge interval of the circuit boards, the presence or absence of the transfer abnormality can be judged for each transferred circuit board.
Further, in the reflow soldering apparatus according to the first mode, when the presence or absence of the transfer abnormality is judged on the basis of the number of circuit boards being transferred, the transfer abnormality can be detected irrespective of thicknesses of the circuit boards and, whether the transfer abnormality results from the clog or drop in the middle of the transfer of the circuit boards by the transfer conveyor can also be judged.